Organic light-emitting diodes (OLED) are commonly used to provide displays in electronic display devices. Typically, OLEDs are driven by an active matrix backplane, i.e. a matrix or array of thin film transistors (TFT) or organic TFTs (OTFT). Each pixel of the OLED display is selectively addressed by an individual TFT of the backplane to change the state of the pixel.
One commonly used pixel circuit for OLED displays comprises two transistors and one capacitor (“2T1C”). One of the transistors is an addressing transistor, while the other is a driving transistor. The addressing transistor transfers voltage from a data line to the gate of the driving transistor. The driving transistor converts the data voltage to a corresponding current for the OLED pixel.
Typically, amorphous silicon or polycrystalline silicon TFTs are used in the pixel circuit, but OLED pixels may also be driven by OTFTs where the channel is made from an organic semiconductor. However, organic semiconductors have low charge mobility, which dictates usage of large transistors to drive OLED pixels. Consequently, the low charge mobility of organic semiconductors means that high-density OLED pixels cannot be as easily achieved compared to amorphous silicon or polycrystalline silicon TFTs.
US2008/237580, US2009/224235 and JP2013254859 describe known structures.
The present applicant has recognised the need to provide a pixel structure which enables the processing of high-density OTFT-driven OLED panels to be operated at low voltages.